From The Independent:
The Lindt & Spruengli company confirmed local reports on Tuesday that there was a minor defect in the cooling ventilation for a line for roasted "cocoa nibs" in its factory in Olten, between Zurich and Basel.
Combined with strong winds on Friday morning, the powder spread around the immediate vicinity of the factory, leaving a fine cocoa dusting.
The Lindt company has confirmed that the chocolate snow was harmless to both people and the environment. The only damage was done to a single car; the company has offered to clean the chocolate flakes off of the vehicle for the owner, but so far, no one's taken them up on that.
Chocolate snow falls on Swiss town after ventilation defect at Lindt factory [Associated Press]